What Is Saw Palmetto?

An herbal remedy for prostate problems in men, saw palmetto (Serenoa repens) is extracted from the purple berries of the American saw palmetto plant.

Claims, purported benefits: Shrinks the prostate; reduces symptoms of benign prostatic hyperplasia (BPH, enlargement of the prostate gland), such as urgent/frequent urination or urinary leaking. In some European countries, saw palmetto is an accepted treatment for BPH.

What the science says: While many studies have been small, short, and/or not well controlled, and some have shown no benefit, the herb has received high marks in several reviews. A review in 2005 by the Cochrane Collaboration concluded that saw palmetto improves urinary symptoms in men with BPH just as well as the drug finasteride—but with fewer side effects, such as reduced sexual functioning.

Nevertheless, the most rigorous research on saw palmetto has yielded disappointing results. A study in the New England Journal of Medicine in 2006 found that saw palmetto extract did not improve urinary flow, quality of life, and other factors in men with BPH. And in 2011, a major study in the Journal of the American Medical Association tested several doses of a standardized extract in middle-aged men over a 72-week period. Even at three times the standard 320-milligram dose, the saw palmetto did not reduce prostate symptoms. In contrast, a Swiss pilot study in Phytotherapy Research in 2013 found that a 320-milligram dose did improve symptoms of BPH; there was no control group, however.

There are many saw palmetto preparations, with widely varying amounts of fatty acids and sterols. Many also contain other ingredients that are of questionable benefit. Thus, products are likely to have different effects. Most studies have used a specific saw palmetto formula available only in Europe. There is no guarantee that products marketed in the United States are equivalent, even if they are “standardized.” No one knows what an optimal dosage of saw palmetto is, but the amount typically used in studies is 320 milligrams a day.

Common side effects: Abdominal pain and nausea have been reported, but no serious side effects have been found. Be cautious about taking saw palmetto if you have a bleeding disorder or are taking blood thinners, though a 2014 review article on the effect of various herbs on warfarin concluded that an interaction is “doubtful.” Do not take it prior to surgery—it may increase bleeding. It may also not be safe to take it with finasteride or some other BPH drugs. Despite concerns that saw palmetto may throw off the results of PSA tests (for prostate cancer), a 2013 study found no such effect.

Our advice: If you are a man who has urinary symptoms and want to try saw palmetto, talk to your doctor first. You need to make sure what you have is BPH. Keep in mind, the best research so far has cast doubt on the effectiveness of saw palmetto.

Health After 50, published by the University of California, Berkeley, School of Public Health, provides up-to-date, evidence-based research and expert advice on the prevention, diagnosis, and treatment of a wide range of health conditions affecting adults in middle age and beyond. It's part of Remedy Health Media's network of digital and print publications, which also include HealthCentral; HIV/AIDS resources The Body and The Body Pro; the UC Berkeley Wellness Letter; and the Berkeley Wellness website.